Funds are requested for a rotating anode x-ray generator and a low temperature crystal cooling device to be installed in the x-ray diffraction laboratory at the Institute for Enzyme Research, University of Wisconsin in Madison. These instruments would be used by five major groups to collect x-ray data, to characterize new crystals and to test for isomorphous heavy atom derivatives. This request is a supplement to a major commitment by the University of Wisconsin to establish a strong group in macromolecular structure and function at the Institute for Enzyme Research. A wide range of biological problems are under investigation and research progress is dependent upon the availability of the requested x-ray diffraction equipment. These projects include the study of proteins involved in electron transport on both a structural and dynamic level using a combination of x-ray crystallography, nuclear magnetic spectroscopy and site-directed mutagenesis (Holden and Markley), the study of enzyme mechanisms using stereochemical analysis, electron paramagnetic resonance spectroscopy and crystallographic techniques (Frey and Reed), the study of lipid binding proteins (Holden), the study of DNA binding proteins (Holden and Rayment) and the study of the molecular basis of muscle contraction (Rayment). A key feature of all these studies is that they use a combination of approaches and techniques to solve biochemical problems. At present there is a long waiting time to gain access to an x-ray diffraction instrument. In addition no low temperature device is available. There are seven major projects described in the following sections that have a total of more than 20 sets of crystals that need to be investigated. Research progress on these projects is currently restricted by lack of access to equipment. The requested x-ray generator and low temperature cooling device would considerably enhance the research effectiveness of the major users and would also strengthen the intellectual overlap between the different groups.